Storage capacitor power supply

ABSTRACT

A long-lived, lightweight, and quickly and precisely charged storage capacitor power supply capable of stably supplying electric power to a load. The power supply has a capacitor block consisting of capacitors connected in series, in parallel or in any combination of series and parallel. The power supply further includes a charging circuit for charging the block, a charging power supply connected with the block via the charging circuit, and a charge-limiting circuit. This charge-limiting circuit detects the voltage across the terminals of the block and limits charging of the block if the voltage reaches a given value. One embodiment of the invention further includes a charge-limiting circuit, a full charge-detecting circuit, and a residual electricity-detecting circuit connected in parallel with the block. The charge-limiting circuit senses that the voltage across the terminals of the block exceeds the given value and causes the charging current to bypass the block. The full charge-detecting circuit senses that the charge-limiting circuit is operated and determines that full charge is attained. The residual electricity-detecting circuit finds the residual electric power from the voltage across the terminals of the block. Another embodiment has a first and a second capacitor block. The voltage across the terminals of the first block is detected. The first block is charged from the second block until the detected voltage reaches a given voltage. The first block supplies electric power directly to the load.

This application is a divisional of copending U.S. patent applicationSer. No. 08/041,543, filed Apr. 2, 1993.

FIELD OF THE INVENTION

The present invention relates to a storage capacitor power supply whichstores electrical power in a capacitor block consisting of a pluralityof electric double layer capacitors connected in series, in parallel orin any combination of series and parallel and supplies electrical powerto a load.

BACKGROUND OF THE INVENTION

Discussions have existed for many years as to whether exhaust gas fromautomobiles with gasoline engines should be controlled because ofproblems with the global environment. In practice, the annual productionof automobiles is still on the upswing but there is no prospect ofreduction in automobile emissions. Under these circumstances, electricvehicles with batteries or solar cells have attracted attention asvehicles producing no exhaust gas. Therefore, there is an urgent need ofearly realization of practical electric vehicles.

In recent years, electric vehicles have begun to be used as vehicles inbusiness applications such as urban-delivery vehicles and garbage truckswhich are not required to travel a long distance continuously or to runat high speeds. Vehicles running at high speeds faster than 100 km/h andtraveling about 200 km continuously have been reported as experimentalvehicles. Furthermore, vehicles which have solar cells on the top of thebody and run while charging the cells have been proposed. In addition,hybrid vehicles driven by both an internal combustion engine and anelectric motor have been proposed.

One promising type of electric vehicle is a vehicle which has no gearingas used in an automobile with an internal combustion engine but drivesthe four wheels independently, using wheel motors. The driving mechanismof this vehicle is simplified. Also, the problems with the operatingcharacteristics and the operability can be solved by coordinating andcontrolling the wheel motors. The greatest technical problem with theelectric vehicle is to realize an ideal power source, i.e., a batteryhaving a capacity comparable to an automotive engine. In order to putthe electric vehicle into practical use, a battery is needed which iscomparable in size and weight to an internal combustion engine and whosecapacity can deliver power comparable to the power delivered by agasoline engine. Furthermore, the battery must be recharged quickly ormust be replaced with a fully charged battery as simply as a supply ofgasoline.

However, no conventional battery can satisfy the above-describedrequirements. One especially great problem is that it takes long for theprior art battery to be recharged. In spite of this fact, the prior artbattery is larger in size and heavier than the internal combustionengine.

An electric double layer capacitor which is smaller in size but largerin capacitance than the prior art capacitor has been developed. Thiselectric double layer capacitor tends to be used to back up a powersupply or for other application. When a large-capacity capacitor such asthis electric double layer capacitor is employed as a storage capacitorpower supply, it has advantages in being lighter and having longer lifethan a lead-acid battery and other batteries. However, if the voltageapplied to the electric double layer capacitor exceeds the ratedvoltage, then the capacitance of the capacitor is immediately reduced.Also, the leakage current increases. In this way, the capacitor isadversely affected. Another disadvantage is that the internal resistanceand the maximum working voltage are not sufficiently controlled. Forthese reasons, positive use of the electric double layer capacitor forpower use is not yet made.

Heretofore, when a secondary battery is recharged, various difficultieshave arisen in precisely detecting the completion of the recharging orknowing how much electricity can still be obtained from the battery.

Various contrivances have been made to detect the completion of therecharging. One method is to set the end voltage at a given voltage.Another method is to estimate the completion from the amount ofelectricity flowed into the battery. A further method is to detect theinstant at which the voltage slightly drops due to the temperaturecharacteristics of the battery after it is recharged for a given time.In spite of these contrivances, the recharging characteristics varywidely according to the conditions of the battery, i.e., depending onwhether the battery is new or old, on the extent to which the batteryages, on the recharging current, and on whether the battery has beenused continuously or was recharged.

Also, various contrivances have been made to measure the remainingelectric power. One method is to measure the terminal voltage whileapplying a given load. Another method is to calculate the amount fromthe amount of electricity charged and discharged. A further method is toestimate the amount from the temperature and the specific gravity of theelectrolyte. However, the battery characteristics vary widely, dependingon the performance of each individual battery, on whether the battery isnew or old, on the history of the use of the battery, on the load, onthe conditions imposed when the recharging is made, and on otherfactors.

As described above, it can be said that hardly any method of preciselydetecting the full charge point at all times is available. Also, hardlyany method of detecting the amount of the residual electric power in thebattery exists. Furthermore, to make effective use of the electric powerof the battery, it is customary to overcharge it to a given level. Also,it is essential to know the amount of the electricity remaining in thebattery. In the future, electric vehicles will be put into practicaluse, and secondary batteries will be used routinely. Under theseconditions, the wasteful consumption of electrical energy due toovercharge will present a problem that cannot be neglected. We mayexpect that the practicability of the battery depends on whether it ispossible to know the distance that the vehicle can still travel.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a long-lived,lightweight storage capacitor power supply which is capable of beingquickly charged and of supplying a regulated voltage to a load.

It is another object of the invention to provide a storage capacitorpower supply which stores electricity efficiently by the use ofcapacitors and supplies electric power to a load.

It is a further object of the invention to provide a storage capacitorpower supply which permits precise detection of full charge point, thuspreventing wasteful overcharge and undercharge.

It is yet another object of the invention to provide a storage capacitorpower supply which makes it possible to precisely measure the amount ofremaining electricity and to reliably know the limit of the operation.

These objects are achieved in accordance with the teachings of theinvention by a storage capacitor power supply adapted to storeelectricity in a capacitor block consisting of a plurality of capacitorsconnected in series, in parallel or in any combination of series andparallel and to supply electric power to a load, said power supplycomprising: the capacitor block connected with the load and supplyingelectric power directly to the load; a charging circuit for electricallycharging the capacitor block; a charging power supply connected with thecapacitor block via the charging circuit; and charge-limiting circuitswhich detect the voltages developed across the capacitors and limitcharging of the capacitors if the detected voltages reach a given value.

One embodiment of the invention further includes charge-limitingcircuits and full charge-detecting circuits connected in parallel withtheir respective capacitors. The charge-limiting circuits cause thecharging current to bypass the capacitors. The full charge-detectingcircuits sense that the charge-limiting circuits are operated and make adecision to see that full charge is attained. In another embodiment, thepower supply further includes a residual electricity-detecting circuit.This residual electricity-detecting circuit consists of a multiplier andan arithmetic circuit. The multiplier takes the voltage developed acrossthe capacitor and produces the square of the taken voltage. Thearithmetic circuit multiplies the voltage by a constant factor. In afurther embodiment, the residual electricity-detecting circuit takes thevoltage developed across the terminals of the capacitor, applies thevoltage to a series combination of a resistor, a voltage regulationelement, and a detecting device, and detects a current according to theresidual electricity by means of the detecting device.

The invention further offers a storage capacitor power supply forsupplying electric power to a load from charged capacitors, said powersupply comprising: a first capacitor block connected with the load andsupplying electric power directly to the load; a charging circuit forelectrically charging the first capacitor block; a second capacitorblock connected with the first capacitor block via the charging circuitand acting as a power supply for the first capacitor block; and acharging control circuit which detects the voltage developed across theterminals of the first capacitor block and controls the charging circuitin such a way that the first capacitor block is charged by the secondcapacitor block until the detected voltage reaches a given voltage.

The novel storage capacitor power supply comprises the capacitor blockconnected with the load and supplying electric power directly to theload, the charging circuit electrically charging the capacitor block,and the charging power supply connected with the capacitor block via thecharging circuit. The voltage developed across the terminals of eachcapacitor is detected. The charge-limiting circuit senses that thisvoltage has reached a given value and limits charging of the capacitor.Therefore, the capacitor block can be used up to the intended maximumvoltage. Hence, the efficiency at which the electrical energy is storedcan be enhanced.

Other objects and features of the invention will appear in the course ofthe description thereof which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram of a storage capacitor power supplyaccording to the invention;

FIG. 2 is a circuit diagram of another storage capacitor power supplyaccording to the invention;

FIG. 3 is a circuit diagram of a further storage capacitor power supplyaccording to the invention;

FIG. 4 is a circuit diagram of the charging control portion included inthe power supply shown in FIG. 3;

FIG. 5 is a circuit diagram of a full charge-detecting circuit in whicha charge-limiting circuit has been inserted;

FIG. 6 shows waveforms illustrating the results of an analysissimulating the full charge-detecting circuit shown in FIG. 5;

FIG. 7 is a circuit diagram of a charge-limiting circuit consisting oftwo stages;

FIG. 8 is a circuit diagram of a full charge-detecting circuitconsisting of two stages;

FIG. 9 shows waveforms illustrating the results of an analysis made bysimulating the full charge-detecting circuit 5 shown in FIG. 8;

FIG. 10 is a circuit diagram of a residual electricity-detecting circuitfor use in a storage capacitor power supply according to the invention;and

FIG. 11 shows waveforms illustrating the results of an analysis made bysimulating the charging and discharging characteristics of an electricdouble layer capacitor.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, there is shown a storage capacitor power supplyaccording to the invention. This power supply comprises a charging powersupply 1, a charging circuit 2, a voltage-detecting circuit 3, acapacitor C having a large capacitance, reference voltage sourcesproducing reference voltages Vr and Vr′, respectively, and switches S1and S2. A load 4 is connected with this storage capacitor power supply.

The capacitor C having a large capacitance is connected with thecharging power supply 1 via the switch S1 and via the charging circuit2. The capacitor C is also connected with the load 4. The capacitor Csupplies electric power directly to the load 4. The charging powersupply 1 which acts to electrically charge the capacitor C can be thecommercial power line. The charging circuit 2 has a voltage convertermeans such as converter. The voltage-detecting circuit 3 compares thevoltage developed across the terminals of the capacitor C with thereference voltages Vr and Vr′ and senses whether the voltage across theterminals of the capacitor C is the fully charged level. If this levelis reached, the voltage-detecting circuit 3 opens the switch S1 andcloses the switch S2. Accordingly, by setting the reference voltageVr+Vr′ to the fully charged level, the large-capacity capacitor C iselectrically charged from the charging power supply 1 via the chargingcircuit 2 while the switch S1 is kept closed until the voltage developedacross the terminal of the capacitor C reaches the fully charged level.When the fully charged level is reached, the switch S1 is opened to stopthe charging. This prevents the voltage applied to the capacitor C frombecoming excessively large compared with the rated voltage. At thistime, the switch S2 is closed to short-circuit the reference voltageVr′. Thus, a dead band is established for the turning on and off of theswitch S1.

As mentioned previously, where a capacitor is used as a power supply, ifthe applied voltage becomes excessive compared with the rated value ofthe capacitor, then the capacitance of the capacitor will immediatelydecrease, the leakage current will increase, and other problems willtake place. To cope with these problems, it is customary to design andmanufacture the capacitor in such a way that allowances are given to thedecomposition voltage and to the maximum working voltage. However, theelectrical energy stored in a capacitor is proportional to the square ofthe voltage and, therefore, it is advantageous to increase the usedhighest voltage as high as possible. In view of these facts, in thepresent invention, the voltage developed across the terminals of thecapacitor is constantly monitored and limited by the switch S1.Consequently, the capacitor can be used up to its maximum voltage.Hence, maximum allowable electrical energy can be stored effectively.

Referring next to FIG. 2, there is shown another storage capacitor powersupply according to the invention. This power supply is similar to thepower supply already described in connection with FIG. 1 except that aseries combination of a transistor TR and a resistor R2 is connected asa bypass circuit for the charging current flowing into thelarge-capacity capacitor C, and that the voltage produced across theterminals of the capacitor C is limited to a voltage set by a voltageregulation device ZD. Also shown is a resistor R1. The voltage set bythe voltage regulation device ZD is selected to be equal to the voltageassumed when the capacitor C is fully charged. In this fully chargedcondition, the transistor TR conducts. The current flowing through theconducting transistor TR varies so as to maintain the voltage developedacross the terminals of the capacitor C at the voltage corresponding tothe fully charged condition. That is, a voltage limiter is formed.

Referring to FIG. 3, there is shown a further storage battery powersupply according to the invention. This power supply comprises acharging AC power supply 11, a charging DC power supply 12, chargingcircuits 13-15, a charging control circuit 16, capacitor blocks A and B,and a reference voltage source producing a reference voltage Vr. A load17 is connected with this storage capacitor power supply.

The capacitor block A is a power supply for supplying electric power tothe load 17. This block A is connected with the load 17 and supplieselectric power directly to the load 17. A large-capacity capacitorhaving a low internal resistance and an energy density which is not veryhigh is used as the capacitor block A. The capacitor block B is a powersupply which electrically charges the capacitor block A. The internalresistance of the block B is higher than that of the block A. Alarge-capacity capacitor having large electrical energy per unit volumeor weight is used as the capacitor block B. The charging circuit 15causes the capacitor block B to electrically charge the capacitor blockA. The charging circuit 15 is composed of a voltage converter means suchas a DC-DC converter. The charging control circuit 16 detects thevoltage developed across the terminals of the capacitor block A, or theload voltage, and compares the detected voltage with the referencevoltage Vr. If the voltage is less than Vr, the control circuit 16controls the charging circuit 15 so as to electrically charge thecapacitor block A from the capacitor block B. The reference voltage Vris set to the level at which the capacitor block A is fully electricallycharged.

The charging AC power supply 11 consists, for example, of an ordinary ACpower line. The charging DC power supply 12 is composed of a DC powersupply such as a stock of solar cells. The charging circuits 13 and 14provide conversion and rectification of the input voltage andelectrically charge the capacitor block B. Of course, the chargingcircuits 13 and 14 can be composed of voltage converter means such asinverters.

As described above, the required power supply capacity is assigned totwo power supply portions, i.e., the capacitor blocks A and B. Onefourth of the total capacity is assigned to the block A, while theremaining three fourths is assigned to the block B. These ratios mayvary according to the load and other conditions. The capacitor block Ais maintained at its fully charged level as faithfully as possible. Inthis way, the load is always supplied with a relatively constant voltagefrom the power supply of the lower internal resistance, or the capacitorblock A. Furthermore, many power supplies, i.e., the capacitors formingthe block B, which are easy to manufacture and have a high internalresistance are employed and so the volume and the weight of the wholestorage capacitor power supply can be suppressed.

FIG. 4 shows an example of the configuration of the charging controlportion of the storage capacitor power supply shown in FIG. 3. Acomparator 21 compares the voltage developed across the terminals of thecapacitor block A with the reference voltage Vr and produces a signalwhich operates the charging circuit 15 when the reference voltage ishigher. Resistors R1 and R2 divide the voltage developed across theterminals of the capacitor block A and detect the voltage. The detectedvoltage is applied to the comparator 21 via a resistor R3. As describedlater, charge-limiting circuits may be connected with their respectivecapacitors of the block A, and the fully charged condition may bedetected. A resistor r is used to detect the charging current. Thecharging circuit 15 cooperates with the resistor r to detect andregulate the charging current. In particular, the charging circuit 15 isturned on and off by the output signal from the comparator 21. Thecharging current is controlled by making use of the detection of thecurrent, utilizing the resistor r. The capacitor block B is a powersupply having a large internal resistance. If the block B iselectrically charged with a large current, the loss will increase. Thisloss is reduced by limiting the charging current.

An electric double layer capacitor used in the present invention is nextdescribed. The electrodes of this capacitor are made of activated carbonwhich has a large specific surface and is electrochemically inactive.The electrodes are combined with an electrolyte to provide a largeelectric double layer capacitance. When the voltage applied between theelectrodes is increased, the electric double layer is formed and thecapacitor is electrically charged until the decomposition voltage of theelectrolyte is reached, whereupon a current begins to flow. Therefore,the maximum working voltage of this electric double layer capacitor isrestricted by the decomposition voltage of the electrolyte. Thedecomposition voltage of the electrolyte of a water solution having ahigh electric conductivity is about 1.23 V. Electric double layercapacitors having maximum working voltages of several volts andcapacitances of several farads are commercially available. The internalresistance values vary widely from 100 Ω to about 10 Ω. A recentexperimental electric double layer capacitor is reported to have 2.5 V,240 F, and 0.1 Ω.

Where the prior art electric double layer capacitor is used as a storagecapacitor power supply, the maximum working voltage is low, and theamount of stored electric charge is small. In addition, the amount ofcharge stored in the electric double layer capacitor is only onetwentieth of the amount of charge stored in lead-acid batteries andnickel/cadmium batteries on the relation between the energy and theweight. Also, the internal resistance of the electric double layercapacitor is large. Therefore, the electric double layer capacitorcannot be used in high power applications. A fundamental method ofpermitting the electric double layer capacitor to rival lead-acidbatteries is to increase the energy density and reduce the internalresistance.

Generally, if a voltage exceeding the decomposition voltage is appliedto a capacitor, decrease in the capacitance, increase in the leakagecurrent, and other problems will occur. Therefore, a voltage lower thanthe decomposition voltage is used as the maximum working voltage. Thedecomposition voltage is 1.23 V for the case of water and about 1.5 to2.5 V for the case of normally used organic electrolytes. On the otherhand, numerous solvents of chemical materials exist which exhibitdecomposition voltages exceeding 6 V in organic electrolytes. However,where they are used in an electric double layer capacitor in practice,the rated maximum working voltage is restricted to 1.5 to 2.5 V. Weconsider that this is due to impurities, including water.

Various foreign substances are naturally adsorbed to porous electrodesconsisting of activated carbon or fibers of activated carbon. If theseelectrodes are used as they are, the various foreign substances aredissolved in an electrolyte when the electrodes are immersed in theelectrolyte. Therefore, if the electrolyte is highly refined, the puritydeteriorates, thus lowering the decomposition voltage. Thus, the foreignsubstances can be removed by previously heating the electrodes in avacuum vessel by RF heating while evacuating the inside of the vessel,then cooling the electrodes as they are, and immersing them in anelectrolyte in a vacuum. Also, decrease in the purity of the electrolytecan be prevented.

In an electrode structure providing a large electrostatic capacitanceand a low internal resistance, activated carbon fibers are activatedslightly excessively to obtain fibers having somewhat large micropores.These fibers are aligned and arranged closely in a plane. A metal suchas aluminum is deposited by evaporation or thermal spraying on both endsand the rear surface of the fiber array, or the electrodes are connectedby a conductive paint or the like. Then, lead wires are attached. Inthis manner, electrodes having a low electrical resistance and a highdensity can be obtained. These electrodes are impregnated with anelectrolyte. The electrodes are mounted on opposite sides of aninsulating porous separator. They are used as positive and negativeelectrodes, respectively.

An electric double layer capacitor having a high maximum working voltagecan be derived by refining the electrolyte and fabricating andassembling the activated carbon electrodes as described above. Also, theinternal resistance can be reduced. As a result, if the maximum workingvoltage is increased by a factor of 2, for example, then the amount ofstored electric charge can be increased fourfold, i.e., the square of 2.The previously mentioned experimental electric double layer capacitor of2.5 V, 240 F, and 0.1 Ω measures 35 mm in diameter by 50 mm. Theelectric energy that can be taken up to 1 V is 0.175 watt-hour(WH). Tosecure an electric energy of 20 KWH required for the power source of anelectric vehicle, a volume of about 6 m³ is needed. As an example,however, the volume can be reduced to one-fourth only by doubling themaximum working voltage. Furthermore, the packaging density can beincreased by a factor of 2.5. The novel storage capacitor power supplyusing two capacitor blocks and the charge-limiting circuits improves theamount of stored charge by a factor of about 2. Also, there is apossibility of increase in the electrostatic capacitance. In this way,the amount of stored charge can be increased by a factor exceeding 20.Such electric double layer capacitors are used in different manners toincrease the stored electrical energy. Also, the internal resistance isreduced to reduce the energy loss. In consequence, the efficiency atwhich electric power is supplied can be enhanced.

In the structure constructed as described thus far, the charging iscontrolled separately for each individual capacitor block. Electricdouble layer capacitors have low maximum working voltage of 2.5 to 5 V.Therefore, where they are used in electric power applications, they areconnected in series. In this structure, if the voltages assigned to thecapacitors are different, the capacitors will successively exceed theirrated values from the smallest capacitor and get damaged. To avoid this,they must be used within voltage ranges lower than the rated values. Inthis case, where charge-limiting circuits are connected with all thecapacitors, respectively, and they are connected in series, if onecapacitor reaches its rated value, the charge-limiting circuit connectedwith this capacitor turns on the bypass circuit, thus preventing all thecapacitors from being applied with voltages exceeding their ratedvoltages. Consequently, they can be used up to the rated voltagessafely. In the novel electric double layer capacitor utilizing anelectric double layer capacitor, a charge-limiting circuit is insertedin each cell to monitor the voltages at the cells and make uniform thevoltages as described above. Examples of the charge-limiting circuit andan example of a full charge-detecting circuit are described below.

FIG. 5 shows an example of the full charge-detecting circuit in which acharge-limiting circuit has been included. FIG. 6 shows the results ofan analysis made by simulating the full charge-detecting circuit shownin FIG. 5. FIG. 7 is a diagram showing a charge-limiting circuitconsisting of two stages. FIG. 8 is a diagram showing a fullcharge-detecting circuit consisting of two stages. FIG. 9 shows theresults of an analysis made by simulating the full charge-detectingcircuit shown in FIG. 8.

Referring to FIG. 5, a charge-limiting circuit and a differentiatingcircuit consisting of CT and RT are connected in parallel with anelectric double layer capacitor C1 having an internal resistance of R1.The charge-limiting circuit comprises a three-terminal shunt regulatorICX1, a transistor Q1, a Schottky diode D1, and resistors R2-R5. Whenthe capacitor C1 is electrically charged from a charging power supply 11and becomes fully charged, the charge-limiting circuit causes thecurrent to bypass the capacitor. This fully charged condition isdetected by the differentiating circuit. This detection is performed bysuperimposing an AC waveform on the charging power supply 11.

FIG. 6 shows waveforms during the charge process of an electric doublelayer capacitor used in power applications. The capacitor, with anelectrostatic capacitance of 300F, maximum working voltage of 50V, andan electric capacity of 100 WH, is charged from completely dischargedcondition by a charging current of 2 A. The voltage across the terminalof the capacitor is indicated by V(1) and the current through theresistor R5 in the charge-limiting circuit is I(R5). The terminalvoltage at the resistor RT in the differentiating circuit is indicatedby V(9) in FIG. 6. A ripple current having a frequency of 10 MHz and anamplitude of 0.5 A is superimposed. This extraordinary low ripplefrequency permits the waveform showing the result of an analysis clearlyin those figures. In practice, ripple current from a rectifier circuitused for AC power line can be used. In FIG. 6, the charging voltageapproaches 50 V when a charging operation persists for 7400 seconds.When the charge-limiting circuit is operated, the current I(R5) flowingthrough the resistor R5 and the terminal voltage V(9) at the resistor RTchange violently. Therefore, a fully charged condition can be easilyknown by detecting these changes.

The configuration shown in FIG. 7 is built for electrical powerapplications as described below. The electric double layer capacitors C1and C11 are connected in series. The charge-limiting circuit consistingof the components R2-R5, X1, Q1, and D11 and the charge-limiting circuitconsisting of components R12-15, X11, Q11, and D11 are connected withthe capacitors, respectively. When each capacitor reaches its ratedcondition, the charge-limiting circuit connected with the capacitorturns on the bypass circuit. Thus, all the capacitors are prevented frombeing applied with a voltage exceeding the rated value. In this manner,the voltages of the cells are monitored and can be made uniform.Consequently, the power supply can be used up to the rated value safely.Furthermore, the fully charged condition can be detected precisely bydetecting the condition in which all the charge-limiting circuitsconnected in series via the differentiating circuit consisting of CT andRT as shown in FIG. 8 have been operated.

In the configuration shown in FIG. 8, the two electric double layercapacitors C1 and C11 are connected in series. A simulation was made inwhich each of these two capacitors C1 and C11 had a maximum workingvoltage of 25 V and an electrostatic capacitance of 600 F, and in whichthe settings of the charge-limiting circuits were intentionally shiftedto about 24 V and 23 V, respectively. The results of this analysis areshown in FIG. 9. That is, the line indicating the whole charging voltageV(1) is bent near the end of the charging process. Observation of theterminal voltage V(9) at the resistor RT of the differentiating circuitand the current I(R5) flowing through the resistor R5 of onecharge-limiting circuit shows that one capacitor is fully charged andthen the other is fully charged.

It can be seen from the foregoing that the following methods can be usedto sense that a storage capacitor power supply having a plurality ofelectric double layer capacitors connected in series, in parallel, or inany combination of series and parallel, has been fully charged. In onemethod, signals are taken from all the charge-limiting circuitsconnected with the capacitors. These signals are ANDed to sense that allthe capacitors have reached their rated conditions. In this state, thepower supply is regarded as being fully charged. In a second method, theoperating points of all the charge-limiting circuits connected with thecapacitors are previously set within a given tolerance, e.g., 5%, usingtechniques of inspection and quality control. One of the capacitors isselected. When the operating point of the charge-limiting circuit forthis capacitor is reached, the power supply is regarded as being fullycharged. In a third method, an AC waveform or a pulse waveform issuperimposed on the currents produced from current regulation circuitsor pseudo-current regulation circuits used for the charging of thecapacitors. The amplitudes are monitored to detect the fully chargedcondition. In this method, the amplitudes decrease suddenly when all thecapacitors connected as loads are fully charged and all thecharge-limiting circuits turn on the bypass circuits. This point isdetected to detect the fully charged condition of the power supply.

Detection of the residual electric power utilized in the novel storagecapacitor power supply is described next. The novel storage capacitorpower supply rarely employs only one electric double layer capacitor. Asdescribed in connection with FIG. 4, plural electric double layercapacitors are connected in series to form a block. Alternatively, suchseries combinations of the capacitors are connected in parallel to forma block. In this case, the residual electric power W is given by

W=0.5•Ca•Va•Va+0.5•Cb•Vb•Vb  (1)

where Ca is the capacitance of the capacitor block A, Va is the voltagedeveloped across the capacitor block A, Cb is the capacitance of thecapacitor block B, and Vb is the voltage developed across the capacitorblock B. Accordingly, the residual electric power can be foundaccurately by measuring the voltages Va and Vb across the blocks A andB, respectively, and introducing these values into an arithmetic unitperforming the above-described calculation.

FIG. 10 shows a residual electricity-detecting circuit used in the novelstorage capacitor power supply. FIG. 11 shows the results of an analysisperformed by simulating charging-and-discharging characteristics. FIG.10A shows a circuit comprising a multiplier X1 and an operationalamplifier U2. The multiplier X1 calculates the square of V. Thecalculated square is multiplied by a constant factor by means of theoperational amplifier U2. In this way, the circuit produces a signalindicating the residual capacity. Where the residual electric powers ofa plurality of electric double layer capacitors or of a plurality ofcapacitor blocks are detected, the multiplier X1 and a resistor R2 areprovided for each capacitor or each capacitor block and connected with anode 3. Thus, a signal indicating the sum of the residual electricpowers can be taken from the outputs from the operational amplifiers U2.In FIG. 10B, a resistor R5, a light-emitting diode D1, and a zener diodeD2 are connected in series with an electric double layer capacitor C2and its internal resistance R4 to roughly represent the residualelectric power by means of a light quantity. The resistor R5 is used asa current-limiting resistor which adjusts the gradient, or thebrightness of the light-emitting diode D1. Of course, an indicator canbe used instead of the light-emitting diode D1. Instead of the zenerdiode, any other voltage regulation device or constant-voltage sourcecan be used as long as it forms a voltage regulator circuit.

The line A of FIG. 11 indicates the voltage developed across theterminals of an electric double layer capacitor having an electrostaticcapacitance of 300 F, a maximum working voltage of 50 V, and an electricenergy of about 100 WH. At the beginning, the capacitor is fullydischarged. Then, it is charged with a current of 2 A. The line B ofFIG. 11 indicates the residual electric power calculated, using theequation described above. A residual electric power meter indicates0.5×300×49×49=about 360 kJ, i.e., 100 WH. The line C of FIG. 11 isobtained by superimposing a straight line on the line B. Thischaracteristic is derived by connecting a zener diode of about 18 V inseries with the terminal voltage V(1). It can be seen that the residualelectric power can be measured with practical accuracy from the fullycharged condition to about three fourths of the range downwardly.

It is to be understood that the present invention is not limited to theabove-described embodiments and that various changes and modificationsare possible. In the above embodiments, the means which turns on and offthe circuit is merely a switch. A semiconductor switching device such asa thyristor or a transistor or other switching device may be used.Furthermore, the application of the novel electric double layercapacitor is not limited to the power supply of an electric vehicle. Forinstance, the novel power supply can also be used as the power supply ofan electric welder or other electrically powered machine, as the powersupply of a portable electrical appliance such as a flash lamp, radioreceiver, television receiver, or video camera.

According to the present invention, as can be seen from the descriptionmade thus far, the charging of each capacitor is controlled to the fullcharge level by the voltage across the terminals of the capacitor.Therefore, the electrical energy can be stored effectively. Also, theefficiency at which the storage capacitor power supply supplies electricpower can be enhanced. Furthermore, the capacitors can be prevented frombeing applied with voltages exceeding the rated voltage. Consequently,where the power supply is used to store electricity, decreases in thecapacitances of the capacitors, increase in the leakage current, andother problems can be prevented.

Having thus described my invention with the detail and particularityrequired by the Patent Laws, what is desired and claimed to be protectedby Letters Patent is set forth in the following claims.

What is claimed is:
 1. A storage capacitor power supply adapted to storeelectricity in a capacitor block consisting of a plurality of capacitorsconnected in series, in parallel or in any combination of series andparallel and to supply electric power to a load, said power supplycomprising a residual electricity-detecting circuit which takes thevoltage developed across the power supply and, applies the voltage to aseries combination of a voltage regulator circuit and a detector devicefor detecting a current corresponding to the residual electric power. 2.In a storage capacitor power supply adapted to store electricity in acapacitor block consisting of a plurality of capacitors connected inseries, in parallel or in any combination of series and parallel and tosupply electric power to a load, said power supply comprising: thecapacitor block connected with the load and supplying electric powerdirectly to the load; a charging circuit for electrically charging thecapacitor block; a charging power supply connected with the capacitorblock via the charging circuit; a charge-limiting circuit which detectsthe voltage developed across each capacitor and limits charging of thecapacitor when the detected voltage reaches a given value; a residualelectricity-detecting circuit comprising: means for detecting thevoltage produced across the capacitor block; a multiplier producing thesquare of the voltage developed across the terminals of the capacitorblock; and calculating means for multiplying the output from themultiplier by a constant factor to provide a number indicative of theresidual electricity in the capacitor block.
 3. In a storage capacitorpower supply adapted to store electricity in a capacitor blockconsisting of a plurality of capacitors connected in series, in parallelor in any combination of series and parallel and to supply electricpower to a load, said power supply comprising: a charge-limiting circuitconnected in parallel with each capacitor and causing charging currentto bypass the capacitor by sensing that a terminal voltage thereof hasreached a given value; a full charge-detecting circuit which detectsoperation of the charge-limiting circuit and makes a decision to see ifa fully charged condition has occurred; a residual electricity-detectingcircuit comprising: means for detecting the voltage produced across thecapacitor block; a multiplier producing the square of the voltagedeveloped across the terminals of the capacitor block; and calculatingmeans for multiplying the output from the multiplier by a constantfactor to provide a number indicative of the residual electricity in thecapacitor block.